The operating temperature within a gas turbine is both thermally and chemically hostile. Significant advances in high temperature capabilities have been achieved through the development of iron, nickel, and cobalt-based superalloys and the use of environmental coatings capable of protecting superalloys from oxidation, hot corrosion, etc. Parts can be fabricated by joining subcomponents including the superalloys. It is desirable to improve weldability based upon liquation and strain age cracking. Improving the weldability can extend the usable life of the parts.
In the compressor portion of a gas turbine, atmospheric air is compressed to 10-25 times atmospheric pressure, and adiabatically heated to 700° F.-1250° F. (371° C.-677° C.) in the process. This heated and compressed air is directed into a combustor, where it is mixed with fuel. The fuel is ignited, and the combustion process heats the gases to very high temperatures, in excess of 3000° F. (1650° C.). These hot gases pass through the turbine, where airfoils fixed to rotating turbine disks extract energy to drive an attached generator which produces electrical power. To improve the efficiency of operation of the turbine, combustion temperatures have been raised. Of course, as the combustion temperature is raised, steps must be taken to prevent thermal degradation of the materials forming the flow path for these hot gases of combustion.
Certain known alloys may be used for components disposed along the flow path of these hot gases. Certain portions of these components must be able to withstand temperatures higher than other portions of these components. For example, certain portions may be resistant to temperatures for adiabatically heated (for example, 800° F.-1250° F.) and other portions may be further resistant to hot gases heated by the combustion processes (for example, in excess of 3000° F.). Components made entirely of alloys resistant to the highest temperature may be undesirable by being overly expensive or by failing to include other properties desirable in other portions of the components. Alternatively, components made entirely of alloys resistant only to the temperature of the lower temperature portions may fail.
A welded component, a welded gas turbine component, and a process of welding a component that do not suffer from one or more of the above drawbacks would be desirable in the art.